Apparatus for producing granulecoated bases



April 27, 1954 M. DORFAN APPARATUS FOR PRODUCING GRANULE-COATED BASES Original Filed Nov. 6, 1946 6 Sheets-Sheet 1 NOH HQ l em D MH Hm. n 0 mm" PH i m April 27, 1954 M. I. DORFAN APPARATUS FOR PRODUCING GRANULE-COATED BASES 6 Sheets-Sheet 2 Original Filed Nov. 6. 1946 M. l. DORFAN April 27, 1954 2,676,562 APPARATUS FOR PRODUCING GRANULE-COATED BASES 6 Sheets-Sheet 3 Original Filed Nov. 6, 1946 April 27, 1954 DORFAN 2,676,562

APPARATUS FOR PRODUCING GRANULE-COATED BASES Original Filed Nov. e. 1946 a Sheets-Shet 4 I as j J 89 M 90 A I 10 1 -se 113 x 66- 112k O FLI x M. l. DORFAN April 27, 1954 APPARATUS FOR PRODUCING GRANULE-COATED BASES 6 Sheets-Sheet 5 Original Filed Nov. 6, 1946 o o oho w m nw o 040 ww w April 27, 1954 M. 1. DORFAN APPARATUS FOR PRODUCING GRANULE-COATED BASES Original Filed Nov. 6, 1946 6 Sheets-Sheet 6 llllll QZUQUJ mumu kwan Patented Apr. 27, 1954 APPARATUS FOR PRODUCING GRANULE- COATED BASES Morton I. Dorian, Pittsburgh, Pa., assignor to Koppers Company, Inc., a corporation of Delaware Original application November 6, 1946, Serial No.

708,096, now Patent No. 2,536,042, dated January 2, 1951. Divided and this application June 1, 1950, Serial N0. 165,561

8 Claims. 1

- The present invention relates to improvements in apparatus for applying coatings to sheet materials, and to methods of operating such apparatus. More particularly, the invention relates to improvements in the production of coated metal sheets having extensive surface areas and to which solid particulate material is bonded for protective, decorative, camouflage or other purposes.

Metal roofing and siding sheets for construc tion of houses, sheds, and other structures are commonly protected against corrosion and other effects of exposure and handling by coating them with heat-liquefiable or thermoplastic compositions such as tar, pitch or asphalt, and by bonding thereto particles of minerals such as slate, mica and the like. In providing a sheet coated with such particles, it is important that the particles adhere uniformly and that they completely and uniformly cover the entire surface of the sheet. This is difficult to attain particularly in large scale, high-speed production.

In the present invention, the above desired uniformity is obtained by various means while effecting an increase in the rate of production and greatly simplifying the apparatus needed for providing the improved results. In order to obtain uniform adherence and coverage of solid particulate substances on the entire surface of a thermoplastic precoat, the latter should be uniformly sticky or uniformly softened over its entire surface and the precoat must remain permanently in position on the surface of the sheet. To prevent sagging it has been found preferable to permit a thermoplastic coating to harden on a sheet before heat is applied to render the coating sticky for bonding solid particulate material, rather than to apply solid particulate material immediately after the sheet is coated with the liquid thermoplastic material or before it has initially set.

To heat the entire surface area or superficies of the thermoplastic coating on a sheet of extensive area at one time and to render the entire coating surface uniformly sticky, hot circulating gases are brought into contact with, and envelope the entire area of the coating. The coated sheet is maintained in such contact for a period sufficient to render the coating sticky without causing it to now, and to maintain it so until the solid particulate material is applied. The method and means of applying heat in the present invention makes it possible to convey coated sheets in vertical position for the application of the solid particulate material to both sides of the sheets with- 2, out the necessity of turning them. The particulate solids projected onto the sticky surface are preferably preheated so that they may more readily become at least partially embedded in the precoat.

The particulate solids or dust particles should, for certain purposes, be of a size to insure thorough coverage of the coated sheet. Since the larger particles are preferable in such cases, smaller particles are removed initially or before recirculation of unused particles. When the smaller particles in a dust are in too great concentration and when they reach and adhere to the sticky surface of a sheet before the larger particles, the smaller particles tend to prevent the proper adherence of the larger, better-covering particles.

The terms dust and solid particulate material as employed herein refer to granules which may he of any suitable size in the range of about 10 to 100 mesh and preferably 10 or 20 to 40 or mesh. Granules employed have surfaces which have any one or more of the following characteristics: curved and shell-like, flat, approxima'tely even planes, very uneven, rough, or irregular. The granules may be made up of natural granules, artificially colored granules, synthetic granules or mixtures of granular substances. Materials most commonly used are slate, greenstone, chert, flint, quartzite, rhyolite, quartz sand,

quartz river gravels, limestone, feldspar, granite. ore tailings, slag, shale, crushed brick and tile, mica, talc, and foliated talc. Asbestos fiber, paper flock, abrasive dusts, organic dusts, and metal powders may also be employed.

Further details of the present invention are described hereinbelow and are shown in the accompanying drawings in which:

Fig. l is a side elevational view of a dusting plant;

Fig. 2 is a top view of the plant shown in Fig. 1;

Fig. 3 is a horizontal section of a portion of the plant including a tunnel in which are combined heating, dusting, and cooling means, and an arrangement of dues for gases that are circulated in the tunnel;

applying means; and Fig. 13 is a front elevation of said mean viewed from a side of a passing sheet under treatment;

Fig. 14 is a side view of a rack for conveying a sheet through the tunnel; and Fig. 15 is a front view of the rack;

Fig. 16 is a view showing a modified arrangement of fiues for the dusting and cooling sections in the tunnel; and

Fig. 1'7 illustrates diagrammatically the operation of apparatus to be described.

Similar parts of the apparatus are designated by the same reference characters in the various figures.

Referring to Figs. 1, 2 and 3, there is shown an elongated, multisection chamber, or tunnel, or enclosure, designated conveniently as a tunnel and generally by the numeral 10. This tunnel includes in series a heating section or chamber H, a dusting section or chamber i2 and a cooling section or chamber i3, each of which is of any suitable shape and dimensions provided with dust-impervious roof and walls. The tunnel I!) is provided with an inlet end I 3 and an outlet end t5. An overhead tracl: It extends the length of the tunnel Hi interiorly from inlet to outlet and exteriorly from outlet to inlet, forming a continuous loop for the rack conveyor or for sheet carriers ii, particularly adapted for use in the present apparatus and more fully described below. Though the outlet i5 is shown at a side of the tunnel, it may be directly at the end and the track It may pass straight through and follow any desired course.

Air or other gases, suitably inert with respect to bituminous coating materials, are employed as heating media in the heating section ii and in the dusting section i2. A furnace is provided with a burner iii heats the gaseous medium, such as air for instance, which is circulated by means of a blower 23 that is rotated by means of a variable speed motor Zl. The blower 2!! is connected to a vertical hot-air feed-pipe 22 which in turn is connected to branch pipes 23 and 24 positioned on opposite sides of the tunnel it, as shown in Fig. 6, adjacent vertically elongated inlet openings 25 and 2%, respectively, opposite each other in the sides of the tunnel between, or at the intersection of, the heating section I i and the dusting section ii. A plurality of branch flues 27 at various levels connect the pipe 23 to the opening 25, and the pipe 2 5 to the opening 26. Each of the fines 27 has an end section 28 that flares outwardly toward the hot air inlet to which it is connected. Also, each of the fines 2? is provided with a slide valve 25 for regulating the hot air supply to the various levels in the tunnel in a manner and for purposes to be described.

Adjacent the inlet end it of the tunnel iii, are hot-air outlets til and 3| opposite each other in the sides of the tunnel and similar to hot-air inlets and 2%. A pipe 32 connects the air-intake end of the furnace it to branch pipes 33 and as which are in turn connected to the hot-air outlets 3B and Si respectively by branch fiues 35 similar to branch flues 27 and in a similar manner. Each of the fiues 35 is provided with a slide valve 36 and a flared section 37.

Circulation of hot-air through the heating section i i is established by the blower 2G and associated pipes and flues, preferably'countercurrent to he direction of travel of sheets under treatment.

An air lock 50 at the tunnel entrance it serves to prevent cold air outside the tunnel from diluting the hot air in the heating section II. As

shown in Figs. 3, 4 and 5, the air loci; is constructed by providing an enclosed air space, at the entrance l, from which air is continuously drawn by an exhaust fan 4i (Fig. 1) while sheets are conveyed through the tunnel in. Heat-resistant yieldable rubber strips or spring metal strips 42 and 43 fastened to the opposite sides of the entrance id extend inwardly across the entrance, and their inner edges meet in a vertical line 44 from the track is to the floor of the tunnel In. Each of the strips 42 and 43 is slit at intervals horizontally and outwardly from the line 44 to form a plurality of flaps 45 which normally keep the entrance I4 closed. The flaps 45 are just long enough to permit the passage of aloadedraclc l'i into the tunnel ill. During such passage, the flaps are bowed or forced aside and then spring back to their normal position thereby closing the entrance after a rack has been moved completely therethrough.

Strips t6 and 41 similar to strips 42 and 43 are afiixed to and extend inwardly from the inner edges of solid, rigid walls 43 and 49 respectively, which are in turn in alignment with the sides of the openings 35 and 3|, respectively, nearest the entrance 1 2. The walls 43 and 49 are spaced from the entrance It and form one side of the exhaust openings 56 and 5!, respectively, to which are respectively connected vertical branch pipes 52 and 53 at the flared ends of the branch fiues 54 similar to flues 2i and 35. Flues 54 are each provided with a slide valve 55. The branch pipes 52 and 53 are connected to the exhaust fan M by means of a pipe at.

In the dusting section i2, means are provided for applying dust to a metal sheet precoated with a thermoplastic material that has been rendered uniformly sticky over its entire surface while passing through the heating section Ii. One form of dust distributing means is shown in detail in Figs. 12 and 13. The latter means comprises a dust chute 58 associated with an air flue 59, both extending vertically from the floor of the dusting section 12 through the roof of the tunnel it. The side walls of the flue 59 are fastened to a vertical side wall of the tunnel. Substantially throughout its height within the tunnel, the wall {iii of said flue, facing the path of a sheet conveyed through the tunnel, is provided with a plurality of small openings iii uniformly spaced one above the other. The chute 58 is fastened to the wall 60 of the flue 59 and is provided with a slot 62 in a wall '63 opposite the wall 60. The slot 62 extends vertically substantially the entire length of the chute 58 inside the tunnel, and is slightly wider than the diameter of the openings 6i. The centers of the openings 6i and the center line of the slot 62 are in a plane substantially perpendicular to the line of travel of a sheet under treatment in the tunnel.

The width of the upper end of the chute '58 is substantially equal to the width of the flue 59, and the side walls 6 3 and S5 of the chute 58, as they extend downwardly, converge so that at the floor of the tunnel the distance between these walls is substantially the width of the slot 62. This convergence of the dust? chute walls tends to maintain the dust at about the same concentration throughout the height of the chute 58. In other words, it is made possible to provide a uniform dispersion or suspension of th dust" adjacent the entire area of a tacky surface of a sheet.

Baflies 66 are provided in the chute 58 tobreak the fall of the dust particles and thus decrease their vertical velocity so that they are more readily forced horizontally toward a sheet. The bafiies 66, as shown in Fig. 13, extend partly across the chute 53 at intervals alternately from the walls 8 1 and 65. They are inclined downwardly from said walls, and the free edge of each is positioned just past or substantially at the center line of the slot t2. When the dust employed consists of particles of a light flaky material, such as mica, or material of relatively low density such as fibrous substances, the baffles are not essential.

A dust spray means is provided on each side of the line of travel of a sheet and preferably substantially equidistant from each side of a sheet in the dusting section I2, as shown in Figs. 3 and 12, for coating both sides of a sheet.

To supply dust to the chutes 58, a Redler conveyor 68, as shown in Figs. 2 and 7, or an enclosed, endless bucket conveyor, carries dust from the dust pit 89 beneath the dusting section I2 to above the roof of the tunnel Ill. The dust is dropped by the conveyor, preferably continuously, into the upper end of each chute 5B and it is distributed equally to these chutes by a divider plate the top edge of which is shown in Fig. 2.

The floor of the dusting section I2 is an opengrating ll so that the sprayed, unused dust settling down in section I? falls into the pit 69 where it is pi ked up again by the conveyor 68 which is driven by a motor 68. Make-up dust is supplied from a bin 72 from which the dust drops into the pit 69.

Air supplied to the dues 59 heated air from the furnace IE and istapped from the pipe 23 through a pipe 55 to a fan '16 driven by a variable speed motor it which forces the hot air under a desired pressure through a pipe TI into the fines 59. An advantage of the use of hot air in the .flues 59 is that it heats the dust so that hot particles thereof will lodge more readily in or on a thermoplastic coating material upon impingement. Each of the lines 59 is supplied with hot air preferably at the same temperature and pressure so that the coating efiect of the dust on both sides of a sheet is more likely to be the same.

Unused dust that is in suspension in the dusting section I2 and that does not readily settle out therein is separated from the air by means of a cyclone separator 88 and by means, in a separator housing 8|, including a filter 82, through which the air is drawn and blown out through a pipe 83 by a suction fan 34 driven by a variable speed motor 84 The cyclone 8!] is connected to outlet openings 85 and 86 (Fig. 3) opposite each other in the sides of the tunnel I0 between or at the intersection of the dusting section I2 and the cooling section I3. Pipes 8? and 88, on opposite sides or the tunnel Ill, and leading to the cyclone separator 8d, are connected to the openings 85 and 86, respectively, by means of branch flues 89, similar to branch flues 27, each having a flared section 90 and a slide valve iii. The pipes 81 and 88 are tapered from the uppermost to the lowermost branch fiues 89 to permit of easier withdrawal of air upwardly to the dust separator system.

The air outlet pipe 93 of the cyclone separator 89 leads into the top of the first section 94 of the separator housing SI in which is provided a vertical bafile 95 having its lower edge 96 above a hopper 91. Some of the dust that is not separated in the cyclone 80 is separated in section 94 as the air passes down one side of the baffle 95 and up the other to the opening 98 leading into the filter section 99 in the separator housing 8|. Any suitable lever, means I06, operated by mechanism (not shown) in space I08 for shaking th dust from the filter 82 may be provided, as for example, such as that shown in Patent No. 1,868,876.

Th filter section 99 is provided with discharge hoppers I! and E62 arranged in line with the hopper 9! and the cyclone discharge hopper I03. A rapping means wit of the type shown in Patent No. 1,775,304 is provided for each of these hoppers. A screw conveyor means IM, driven from any suitable power source, is positioned beneath these hoppers for receiving the dust discharged therefrom. The dust from these hoppers is generally progressively finer as the air current passes from the cyclone do to the far end of the filter section 99, and is thus classifled for reuse in the coatin operation. The larger particles from the cyclone 8i] and from section 9:! are passed by the conveyor IM to a conveyor m5 which drops the dust into a chute for introduction into the hopper I2.

A portion of the blade Ill? of the conveyor I04 is so arranged that the dust from the hopper I83 of the cyclone 8t is pushed either into the conveyor IE5 or beyond the conveyor I to a conveyor N19. The dust from the hopper 91 drops into the conveyor Hi l and may then drop into either the conveyor I or the conveyor I09. Th dust from hoppers Iill and I02 drops into conveyor Iild and then into conveyor I09. The end portion III of the conveyor blade extending from beneath the hopper 2 to the conveyor Its is arranged to push the recovered dust from hopper IE2 to conveyor I09.

A chute 5 l2 connects the discharge end of the conveyor N35 with the hopper l2, A chute H3 having a slide valve H4 connects the discharge end of the conveyor N39 with the hopper l2 and is provided with a branch chute IE5 having a slide valve I I6.

In certain instances, particle size is a criterion in a dusting operation and it is desirable in such cases to return only the larger particles to the dusting chamber I2. When the larger particles of a dust, satisfactory for a particular coating, settle in the cyclone hopper I63 and in hopper 9i, and when the finer particles, of smaller and less desirable size, settle in hoppers Hill or I02 or both, as is generally the case in the use of mica for instance, the conveyors IM and I95 are put into operation so that the larger particles will b conveyed to the chute i I 2. With conveyor I69 also in operation, and with slide valve H4 in chute H3 closed and slide valve H6 in chute H5 open, the smaller particles are discarded and are not returned to the hopper I2. By closing the valve lie and opening the valve II l all of the recovered dust may be returned to the hopper I2.

If, for certain purposes, attritional dust or very fine particles of the dust are not desirable ior a particular surface coating, or if the recovered dust is not to be used in the dusting chamber, all of the recovered dust may be discarded through chute I it: by stopping the operation of conveyor IE5, by operating conveyors I04 and IE9, by closing the valve I Hi, and by opening valve H6.

For purposes of assisting in controlling and distributing air currents in the sections II, E? and [3, a damper means is placed at each of the 7, openings 25, 26, 85 and 86. This damper means, illustrated in Figs. 3, 9, and 11, includes a damper plate I29 extending vertically from the bottom to the top of each of these openings. One vertical edge of a damper plate I is affixed to a rotatable vertical rod IZl, serving as an axis, positioned in the tunnel It adjacent an opening so that the free vertical edge H22 of the damper can be swung in an are from one side of the opening to the other. By setting a damper in a predetermined position in the openings and 25 for instance, a portion of the entering gaseous heating medium may be diverted by the damper I28 into the dusting chamber and the remainder into the heating chamber or all of the medium may be diverted into the heating chamber by setting the free edge 222 of the damper tightly against the side of each opening 25 and 26 near est the dusting chamber. The rod IZI extends through the roof of the tunnel II). A lever I23 above the roof engages the rod I2I for operating the damper. The position of the lever readily indicates the position of the damper. Metal bracing plates I25 and I26 maintain the rod I2I in position in the tunnel I I].

In alignment with the ares of each pair or" the dampers IE6 at either end of the dusting section I2, are solid, rigid walls IZl and I28 which extend from said axes on either side to within a short distance from the center line of the tunnel 10, as shown in Fig. 3. In order to maintain the dusting section I2 as well enclosed as possible during the passage of racks I; of the carrier therethrough, a rubber strip or a spring metal strip I29 (Figs. 3, 6 and 8) similar to strip 36 is fastened to each of the walls i2? on the rack side of the carrier. A rubber strip is preferably not placed on the sheet side because of the tendency to mar the heat-softened surface of a coating on the sheets under treatment.

The racks I'l, shown in Figs. 1, l4 and 15, are supported on rollers I39 on the track It and are suspended substantially vertically therefrom. The racks are driven in spaced relation to each other by any suitable means as a chain drive itGA in association with a power mechanism, designated generally by I3I, of any desired type. A rack comprises a trapezoidal frame having side bars I32 and I33, and tapering from the lower end to the top cross bar I3 3. Bracket means !35 at the lower end of the frame serves to support the lower edge of a sheet under treatment away from the plane of the side bars so that the sheet may lean against the frame and be held by its own weight, as shown in Fig. l, with metal sheet material I35. Suitable means for further securing the sheet on a rack may be provided if found necessary. An important consideration is that a sheet should be exposed as much as possible so that its entire surface is readily accessible to the dust material applied in the tunnel. If only one side of a sheet is to be coated with "dust in the dusting section I2, a metal blocking plate may be temporarily placed across the slot 62 of the dusting means on the side of the sheet that is to remain uncoated. Duets of higher specific gravities are particularly suitable for application in this manner.

For purposes of determining conditions in the tunnel l0, thermometers, readable from the outside thereof, are placed at various levels. A thermometer i 38 (Fig. 1) near the bottom and top of the heating-section ii and dusting section I2, and one midway between, serve to indicate whether 'sufficiently uniform temperature 8. conditions are being maintained at the various levels. A thermometer I39 is also mounted on the hot-air feed pipe 22 just above the blower. for indicating the initial temperature of the air passing from the furnace to the tunnel I0.

A pressure indicating device Mil is mounted on the outside of the tunnel Ill to indicate the pressure in the heating section on a scale IM and the pressure in the dusting section on a scale The walls and roof of the tunnel I9, particularly the heating and dusting sections, and the various hot-air conducting means are heat in sulated. A heat insulating layer I43 is shown in Fig. 9 by way of illustration.

By way of a. modification, to further improve the cooling effect in the cooling section I3 of the tunnel Ill, instead of having only one opening for withdrawing dust-laden air from the dusting section I2, and for drawing cooling air through the cooling section, a separate pipe c0n-' nection, similar to pipes 537 and 8B and their branch fiues, is provided for each of two pairs of opposite openings lei ISI (for the dusting" chamber), and 52, I53 (for the cooling chamber). The air withdrawn passes to the cyclone by way of pipe i5 Instead of employing vertical damper means in this case, a partition means similar to that designated by the numerals 43 and 49 (Figs. 3 and 4) is placed between the pairs of said openings, except that a sealing strip is omitted on the side of the rack on which a sheet is placed.

In the operation of the apparatus of the present invention, the racks Il' are moved along the track it at a suitable rate as they pass by a loading platform 55% near the entrance to the tunnel It, a metal sheet, precoated with a thermoplastic coating that is capable of being ren-- tiered. sticky by heat, is placed in vertical position on each rack. The loaded racks are conveyed in succession continuously through the length of the tunnel lil wherein the coating is heated in the heating section I I to provide a uniformly sticky surface over the entire area of the sheet; the sheet bearing the sticky surface is uniformly sprayed with a dust in the dusting section l2; and the dusted sheet is then cooled in the cooling section 53. Upon emerging at the outlet of the tunnel 50, or at any point beyond the outlet, a sheet is substantially ready for use and is removed from the rack. The rack returns to the platform 555 where it is reloaded.

The general operation is somewhat graphically represented in Fig. 17 of the accompanying drawings. Reference to this figure may be made in conjunction with the other figures showing detai s of the apparatus.

While passing thermoplastic coated sheets through the several sections in succession in the tunnel I0, air or other suitable gas, heated to a desired temperature, is introduced through the openings 25 2B in opposite sides of the tunnel between the dusting section I2, and the heating section II. Some of the hot-air passes on both sides of the sheets into the dusting section and is maintained uniformly circulated therein at uniform temperature in contact with the entire tacky surfaces of the sheets; but a larger proportion of "he hot air passes on both sides of the sheets from the openings 25 and 26 into the heating section and is therein also maintained uniformly circulated at uniform temperature in contact with the entire surface of the coatlns that is to be rendered tacky. Simultaneously with these operations, the hot air is drawn through the heating section on both sides of the sheets countercurrent to the direction of travel of said sheets; hot air is drawn through the dusting section concurrently with the sheets; the dust is blown onto both sides of the sheets in the dusting section; the dust-laden air is withdrawn from the dusting section through openings 85 and 86 in opposite sides of the tunnel; and a cooling air current is drawn through the cooling section countercurrent to the direction of travel of the sheets and on both sides thereof, leaving either through openings 85 and [35, or through auxiliary openings I52 and I53 (Fig. 16) by way of modification. Other operations may proceed simultaneously with the above operations and either continuously or intermittently, as for instance, the classification of the dust in the dust separating apparatus and the refeeding of recovered dust into the dusting section, which has been described hereinabove. The entire apparatus is capable of operating as a unit While eifectively preventing escape of dust into the surrounding atmosphere.

Referring to the operation of the apparatus more in detail, the control of the flow and distribution of heating gas to obtain uniform temperature conditions throughout the heating section is of utmost importance. For any given heating temperature, the gaseous heating medi- 'um is preferably so distributed that the entire area of both sides of a thermoplastic coated metal sheet is heated at substantially the same temperature to render the surface of the thermoplastic coating uniformly soft or uniformly sticky over its entire area.

A manner of accomplishing this in the heating section I l of the tunnel It), particularly when temperatures employed are in the higher ranges for treating certain bituminous coatings, is to introduce a greater portion, or preferably all, of

of the heating section, is then, in larger proportion'or'preferably substantially entirely, withdrawn near the bottom of the openings 30 and 3 l. The fan 20 is of a capacity to cause cyclic passage of the heating gas at the proper velocity from the furnace [8 through the heating section it and back through the furnace.

The course taken by the heating gas in the heating section H depends largely on the point 1 or points of introduction and withdrawal of the heating gas, and its velocity of throughput. With the equipment shown in the accompanying drawings, the course of the heating gas is controlled by means of the fan [8 and by means of the valves 29 in the branch lines 27 of pipes 23 and 24, and the valves 36 in the branch fiues 35 of pipes 33 and 34. By adjusting valves 29, the .heating gas is either entirely introduced into the heating section H through the bottom flues 21 connected to the lower end of each of the openings 25 and 28 as indicated in the preferred opwith ste -i eh' e g s i tr d through openings 25 and 25 in varying proportions at the various levels of the flues 21, as for instance in decreasing proportions from the bottom flue to the top flue. The withdrawal of the heating gas from the heating section is controlled by correspondingly adjusting the valves 36 in the fines 35.

The vertical dampers lZil are adjusted at both ends of the dusting section i2 by means of levers [23 to control the flow through said section of hot gas entering the tunnel l!) at openings 25 and 26. Most of the gas'entering the dusting section is drawn through from the heating section directly in contact with the sheet surfaces and directly along the line of travel of the sheets. This not only maintains the sheets at the proper temperature and maintains the sheets uniformly tacky to the point of application of the dust, but also prevents dust from escaping into the heating section from the dusting" section. The operation of means for applying and for handling the dust has previously been described.

The dust is further prevented from escaping into the cooling section 13 by adjustment of the vertical dampers I293 at the junction of the dusting section and the cooling section. The dampers are here set to cause the cooling air to be drawn from the exit 15 along the line of travel of the sheets and on both sides thereof, partly through the opening between the walls l2? and 82s and then through the openings 85 and 86, and partly directly from the cooling section through the openings 85 and 86.

Dust is also kept from seeping out of the dusting section by maintaining a slight vacuum therein or by maintaining a slightly higher pressure in the heating section than in the dusting section. A difference in pressures of about .10 inch in the heating section and in the dusting section is found to be satisfactory. Assuming that the valves 9! are all set, the pressure in the dusting section may be maintained lower than that in the heating section by means of proportioning the air supply with the dampers lZB so that most of the air from pipes 23 and 24 will fiow into the heating section, and/or by increasing the rate of withdrawal of air from the dusting section by means of the suction fan 84.

To help prevent the stacking effect and to overcome normal Stratification effects in the dusting section and thereby maintain uniform temperature in the latter section at various levels on both sides of the sheets, the valves 9! in the branch flues 39 on both pipes 8'! and 8% are adjusted. As in the heating section, and while operating it in a preferred manner described above, a desired effect is obtained by Withdrawing all or most of the gases from the dusting section through the lower end of each of the openings 35 and 86. This can be accomplished by opening wide the lowermost valve 9| on each side and completely or partially closing the upper valves 9! on each side.

The thermometers at the various levels in the heating section II, as well as in the dusting section l2,'are watched by the operator, and adjustments are made to maintain substantially no differences in temperature between the upper and lower levels.

The operating temperatures employed may be widely varied and depend on (1) the rate of feed of sheet material through the heating and dusting sections, (2) the softening-point of the thermoplastic coating, (3) the temperature of the coated article upon entering the heating section, 4 the gauge or thicknessof the metal sheet employed as a base, and (5) the temperature of the atmosphere outside of the heating and dusting sections. In general, the temperature in these sections should not be too high to cause melting or flowing of the thermoplastic coating and should preferably be such that only the outer surface of the coating is heated while the metal of the sheet remains at a relatively low temperature.

In general, for large quantity production a precoated metal sheet is conveyed through the heating and dusting sections of the tunnel shown, at the highest speed at a temperature that will result in satisfactory adhesion of particles to the coated sheet. A relatively short period of preheating in the heating section at a fairly high temperature is generally the aim of the operator,

though" this may vary depending, among other things, on the nature of the thermoplastic coating. speed that provides for a period of heating in the heating section of about 0.8 minute to 2 /2 minutes at about 300 to about 400 F. and in the dusting section of about 0.6 minute to about 2 minutes at about 240 to about 290 F. is suitable for certain. thermoplastic coatings on flat or corrugated metal sheets of 18 to 23 gauge. Speeds of from about 6 feet per minute to about 18 feet per minute have been employed in the tunnel It.

A preferred thermoplastic coating comprises a material that can be applied by dipping or by spraying while in molten condition; that dries and hardens relatively quickly and becomes substantiaily non-tacky at ordinary atmospheric temperatures; that has strong adhesive powers and becomes sticky on heating; that does not flow readily on metal surfaces in vertical position during the period of heating in the abovedescribed tunnel; that becomes sticky on heating before it commences to flow; and that has a relatively high softening-point, (above about 90 0.), relatively high penetrations (above at 32 F. with 200 gms. 60 seconds, and relatively low penetrations (below '70) at 115 F. with gms. 5 seconds, so that it will not be too brittle at freezing temperatures and will not flow on vertical metal surfaces at highest atmospheric temperatures (130 F.) or when exposed to atmospheric conditions. In cases where a coating fiows comparatively readily when heated to render it sticky, a sheet coated therewith may be conveyed through the tunnel at a high enough speed so that flowing is avoided.

Pitches and asphalts and other thermoplastic materials used in coating compositions having the above preferred characteristics are particularly applicable in the above-described process. Coal-digestion pitches prepared by digesting coal in oil or tar at temperatures of approximately 300 to 310 C., and by dispersing the coal, which is preferably thermally decomposed, in the bituminous medium, are highly satisfactory particularly when they contain heavy hydrocarbon oil and coal in proportions that give a composition of the above-mentioned preferred softening-point and penetration ranges. By way of example, reference is made to U. S. Patent No. 2,395,041, to William F. Fair, Jr., for compositions of this type. When heating coatings of coal-digestion pitch, having the above preferred softening-point and penetration characteristics, on a metal sheet, they may initially become soft in certain ranges of temperature and yet in those 12 ranges they do not flow even on vertical metal surfaces.

The following example illustrates more specifically the present process:

Flat or corrugated metal sheets of the type generally employed for roofing or siding, and coated with coal-digestion pitch having a softeningpoint of about to about C. and penetrations at 32 C. above substantially 10 and at 115 F. below substantially 70, are placed on the racks fl and are conveyed through the tunnel it at a speed of about 12 to 17 feet per minute. This corresponds to a period of time in the heating section ll of about 0.9 minute to about 1 minutes, and in the dusting section of about 0.6 minute to about 0.8 minute. The temperature in the heating section is between about 300 F. and about 400 F., or more particularly at about 350 The temperature in the dusting section is between about 240 F. and about 290 3 or more particularly at from about 260 F. to about 230 F.

The entire surface of each vertically supported, pitch coated sheet is exposed in the heating section to asubstantially uniform temperature over the extent of the surface area of the coating to render the surface of the coating substantially uniformly sticky throughout. Whilev this uniform stickiness is maintained in the dusting section, the solid, particulate material such as mica, or other particulate material mentioned above, is impelled toward and impinges and is uniformly spread on the uniformly sticky surface of the coating. The dust-coated sheets then pass into and through the cooling section where they are quickly cooled by currents of cooling air contact with and uniformly spread over the entire coated surface. The thermoplastic coating hardens uniformly and forms a solid bond for the particulate material.

The dusts employed comprise, generally, a substance or substances, solid colored or varicolored, insoluble in water and other solvents, inert with respect to the thermoplastic material provided as a bond, inert with respect to the gaseous heating medium circulated in the tunnel, and non-fusible at the temperatures in the tunnel. Other properties of said dusts have been hereinbefore pointed out.

In the above-described invention, large sheets re easily treated in a relatively sma11 space, without the need for complicated mechanisms and with very little handling by workmen. In treating such sheets in vertical position, accumulation of dust on a sheet is avoided, and yet in a single dusting treatment dust-coated sheets are obtained which are free from defects such as bare spots or uncoated areas, and such as wrinkles due to sagging. Uniform stickiness of the ntire area of athermoplastic precoa-t on a sheet, effectively provided in this invention by uniform heating of said area, assures uniform coverage by uniform distribution of the dust during maintenance of said uniform stickiness.

This application is a division of application Serial No. 708,096, filed November 6, 1946, for A Method of Producing a Granule-Coated Base, now Patent No. 2,536,042 issued January 2, 1951.

The invention as hereinabove set forth is embodied in particular form and manner but may be variously embodied Within the scope of the claims hereinafter made.

What is claimed is:

1. In apparatus for coating sheets with granules, which apparatus includes a multisection 13 chamber having in series a heating section, a granule-applying section and a cooling section, wherein a sheet precoated with a thermoplastic coating is heated in the heating section to render the surface of the coating sticky and granules are applied to the sticky coating in the granule-applying section and the resulting sheet is cooled in the cooling section, and said apparatus having conveyor means for conveying said sheets in vertical position successively through the respective sections from an inlet to an outlet of said chamber; elements comprising: fines, for introducing gaseous heating medium into said chamber, connected to said chamber at the intersection of the heating section and the granule-applying section; means for diverting a portion of the introduced gaseous heating medium into the said heating section and a smaller portion of said medium into the said granule-applying section for providing a greater pressure in the said heating section than in the said granule-applying section to prevent escape of granules from the said granule-applylng section through the said heating section; fines connected to said chamber at the intersection of the granule-applying section and the cooling sec" tion; and means connected to said last-named dues for drawing air into said latter flues from the said outlet of the chamber and through the cooling section in contact with the sheets towards the granule-applying section to cool the sheets and also to prevent the escape of granules from the granule-applying section through the cooling section.

2. In apparatus for coating sheets with granules, which apparatus includes a multisection chamber having in series a heating section, a granule-applying section and a cooling section, wherein a sheet precoated with a thermoplastic coating is heated in the heating section to render the surface of the coating sticky and granules are applied to the sticky coating in the granule-applying section and the resulting sheet is cooled in the cooling section, and said apparatus'having c-onveyer means for conveying said sheets in vertical position successively through th respective sections from an inlet to an outlet of said chamber; the elements comprising: fines, for introducing gaseous heating medium into said chamber, connected to openings in either side of the chamber at the intersection of the heating section and the granule-applying section; means for diverting a portion of the introduced gaseous heating medium at said openings into the said heating section and a smaller portion of said medium into the said granule-applying section for providing a greater pressure in the said heating section than in said granule-applying section to prevent escape of granules from the said granuleapplying section through the said heating section; flues connected to openings in either side of the said chamber at the intersection of the granule-applying section. and the cooling section; and means connected to said last-named flues for drawing air into said latter flues through the outlet of th chamber and through the cooling section in contact with both sides of the sheets towards the granule-applying section to cool the sheets and also to prevent the escape of granules from the granule-applying section through the cooling section. i

3. In apparatus for coating sheets with granules, which apparatus includes a multisection chamber having in series a heating section, a granule-applying section and a cooling section,

wherein a sheet precoated with a thermoplastic coating is heated in the heating section to render the surface of the coating sticky and granules are applied to the sticky coating in the granule-applying section and the resulting sheet is cooled in the cooling section, and said apparatus having conveyor means for conveying said sheets in vertical position successively through th respective sections from an inlet to an outlet of said chamber; elements comprising: a plurality of dues arranged one above the other and connected at various levels from adjacent the bottom to adjacent the top of the said chamber to a vertical elongated opening positioned in each side of the said chamber at the intersection of the heating section and the granule-applying section for conducting gaseous heating medium into each of said latter sections; similarly arranged flues connected to similar openings positioned in opposite sides of said chamber adjacent the inlet thereof and to similar openings positioned in opposite sides of said chamber at the intersection of the granuleapplying section and the cooling section for withdrawing said gaseous medium from said heating section and from said granule-applying section; and valve means in each flue for controlling and varying the flow of said gaseous medium into and out of said sections whereby said medium is uniformly distributed over the surfaces of said precoated sheets to render and maintain said surface uniformly sticky.

In apparatus for coating sheets with granules, which apparatus includes a multisection chamber having in series a heating section, a granule-applying section and a cooling section, wherein a sheet precoated with a thermoplastic coating is heated in the heating section to render the surface of the coating sticky and granules are applied to the sticky coating in the granule-applying section and the resulting sheet is cooled in the cooling section, and said apparatus having conveyor means for conveying said sheets in vertical position successively through th respective sections from an inlet to an outlet of said chamber; elements comprising: flues, for introducing gaseous heating medium into said chamber, connected to said chamber at the intersection of the heating section and the granule-applying section; means for diverting a portion of the introduced gaseous heating medium into the said heating section and a smaller portion of said medium into the said granule-applying section for providing a greater pressure in the said heating section than in the said granule-applying section to prevent escape of granules from the said granule-applying section through the said heating section; flues connected to said chamber at the intersection of the granule-applying section and the cooling section; means connected to said lastnazned fines for drawing air into said latter lines from the outlet of the chamber through the cooling section in contact with the sheets towards the granule-applying section to cool the sheets and also to prevent the escape of granules from the granule-applying section through the cooling section; means associated with said secondnamed flues for separating attritional granule particles from larger particles drawn into said fines from the granule-applying section; and means for returning said larger particles to said granule-applying section for application to said sheets.

5. In apparatus for coating sheets with granules, which apparatus includes a multisection chamber having in series a heating section, a

granule-applying section and a cooling section, wherein a sheet precoated with a thermoplastic coating is heated in the heating section to render the surface of the coating sticky and granules are applied to the sticky coating in the granule-applying section and the resulting sheet is cooled in the cooling section, and said apparatus having conveyer means for conveying said sheets in vertical position successively through th respectivesections from an inlet to an outlet of said chamber; elements comprising: lines, for introducing gaseou heating medium into said chant her, connected to said chamber at the intersection of the heating section and the granule-applying section; means for diverting a portion of the introduced gaseous heating medium into the said heating section and a smaller portion of said medium into the said granule-applying section for providing a greater pressure in the said heating section than in the said granule-applying section to prevent escape of granules from the said granule-applying section through the said heating section; fiues connected to said chamber at the intersection of the granule-applying section and the cooling section; means connected to said lastnamed fiues for drawing air into said latter lines from the outlet of the chamber through the cooling section in contact with the sheets towards the granule-applying section to cool the sheets and also to prevent th escape of granules from the granule-applying section through the cooling section; flue means connected to said first-named fines and to said granule-applying section for conducting heated gas into said section for impinging particles of granules against the sticky sheets to coat the same therewith.

6. In apparatus for coating sheets with granules, an enclosure through which a sheet precoated With a thermoplastic coating is passed in a substantially vertical position, means for conveying said sheet in said position through said enclosure, means for projecting granules within the enclosure uniformly on the coating on both sides of said sheet; means comprising flues connected at the entrance of the enclosure on both sides of the line of travel of the said conveying means and means for controlling the flow of hot gases from said fiues into said enclosure at diflerent levels in contact with both sides of the sheet, and means comprising fiues connected at the outlet of the enclosure on both sides of the line of travel of the said conveying means and means for controlling the flow of gases out of the enclosure at different levels through said lastnamed flues, for distributing the heat of said gases uniformly in said enclosure.

7. In apparatus for coating sheets with granules, an enclosure through which a sheet precoated with a thermoplastic coating is passed in a substantially vertical position, means for conveying said sheet in said position through said enclosure, means for projecting granules within the enclosure uniformly on the coating on both sides of said sheet, means for introducing hot gases into said projecting means for heating and projecting the granules onto said sheet; means comprising flues connected at the entrance of the enclosure on both sides of the line of travel of the said conveying means and means for controlling the flow of hot gases from said flues into the said enclosure at different levels in contact with both sides of the sheet, and means comprising flues connected at the outlet of the enclosure on both sides of the line of travel of the said conveying means and means for controlling the flow of gases out of the enclosure at different levels through said last-named fines, for distributing the heat of said gases uniformly in said enclosure.

8. In apparatus for coating sheets with granules, an enclosure, means for supporting within said enclosure a sheet having a thermoplastic coating thereon, means comprising adjustable inlet openings for introducing a gaseous heating medium in variable volumes at different levels in the enclosure for maintaining the temperature substantially uniform over the entire coating on said sheet, means for feeding granules into the enclosure and separate juxtaposed hot air blast means for forcing heated air against the surfaces of said fed granules to project them in heated condition toward the said thermoplastic coating on said sheet.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 1,873,213 Overbury Aug. 2-3, 1932 1,952,502 Kinkead Mar. 27, 1934 2,217,724 Birmingham Oct. 5, 1940 2,235,978 Braucher Mar. 25, 1941 2,279,686 Kerlin Apr. 14, 1942 2,287,837 Smyser June 30, 1942 12,358,138 Blandchard et a1. Sept. 12, 1944 2,400,315 Paasche May 14, 1946 2,419,835 Hester Apr. 29, 1947 2,536,042 Dorfan Jan. 2, 1951 

